In a material constituting a member to which a built-in heat source or a heat source is attached such as a chassis or a metal base print circuit board for use in a PDP (plasma display), an LCD (Liquid Crystal Display) or a note-type personal computer, it is required to be excellent in thermal conductivity for quick heat dissipation as well as excellent in strength. Furthermore, since the heat load of such a member has increased greatly in recent years because of the improved performance, the increased complication, the miniaturization and the increased density of such a heat source, it is also required that the thermal conductivity and the workability of such a heat source are improved.
In cases where the aforementioned member is made of aluminum, pure aluminum series alloy such as JIS 1100, JIS 1050 or JIS 1070 aluminum alloy is suitably used as a material having high thermal conductivity. However, these alloys are poor in strength. On the other hand, JIS 5052 aluminum alloy adopted as high strength material is remarkably lower than pure aluminum series alloy in thermal conductivity. Furthermore, Al—Mg—Si series alloy is excellent in thermal conductivity and can be improved in strength by conducting age-hardening. Such Al—Mg—Si alloy is, however, required to be subjected to complicated processing such that the alloy is rolled at high temperature, then the rolled alloy is subjected to solution treating, and thereafter the solution treated alloy is subjected to aging treating. Even if high strength can be obtained, there are defects such that the formability such as bendability or stretchability deteriorates extremely (see, e.g., Japanese Unexamined Laid-open Patent Publication Nos. 8-209279, 9-1343644 and 2000-144294).
Under the circumstances, the present applicant has proposed technique for manufacturing an Al—Mg—Si series alloy plate in which rolling conditions of hot-rolling are regulated to thereby obtain both the thermal conductivity and the strength without performing solution treatment and aging treatment (see, e.g., Japanese Unexamined Laid-open Patent Publication Nos. 2000-87198 and 2000-226628).
The aforementioned technique, however, requires complicated condition management such that, in any one of passes for hot-rolling, the material temperature immediately before the pass, the cooling rate between passes, the material temperature immediately after the pass and the thickness of the material immediately after the pass and the reduction ratio at the subsequent cold-rolling are controlled.
Furthermore, the workability of obtained alloy plate does not fully meet the commercial demands. In cases where the forming is performed under severe conditions, it was necessary to pay special attention to the processing facility and the processing method.
In the meantime, it is known that aluminum alloys ranging from JIS 1000 series aluminum alloy to JIS 7000 series aluminum alloy have an excellent correlation between thermal conductivity and electrical conductivity. When performing a regression analysis of the relation between the thermal conductivity and the electrical conductivity of the aluminum alloy shown in FIG. 2, the regression equation: y=3.5335x+13.525 and the determination constant: R2=0.981 can be obtained. This shows extremely high correlation. Accordingly, an aluminum alloy plate having excellent thermal conductivity is also excellent in electrical conductivity, and therefore the alloy plate can be used not only as a heat dissipation member material but also as a current carrying element material.